Secondary battery having sealing portion of novel structure

ABSTRACT

Disclosed herein is a plate-shaped secondary battery constructed in a structure in which an electrode assembly of a cathode/separator/anode structure is mounted in a battery case, and the battery case is sealed by thermal welding, wherein the battery case is provided at a sealing portion around an electrode assembly receiving part thereof with an exhaust guide sealing portion configured in a structure in which a width of the exhaust guide sealing portion decreases from an inside of the sealing portion toward an outside of the sealing portion such that a sealing force of the exhaust guide sealing portion is first released, when high-pressure gas is generated in a battery cell, and therefore, the high-pressure gas is exhausted outside, the exhaust guide sealing portion being thermally welded with a sealing force less than that of a sealing portion located at a remaining region (‘a remaining sealing portion’), and the battery case is further provided at a middle of the exhaust guide sealing portion with a bridge sealing portion extending in parallel to the electrode assembly for interconnecting opposite sides of the remaining sealing portion with a predetermined width, the bridge sealing portion being thermally welded with a sealing force greater than that of the exhaust guide sealing portion.

FIELD OF THE INVENTION

The present invention relates to a secondary battery having anovel-structured sealing portion, and, more particularly, to a secondarybattery including an exhaust guide sealing portion formed at a sealingportion of a battery case in a structure in which the width of theexhaust guide sealing portion decreases from the inside of the sealingportion toward the outside of the sealing portion, the exhaust guidesealing portion exhibiting a low sealing force, and a bridge sealingportion formed at the exhaust guide sealing portion, the bridge sealingportion exhibiting a relatively high sealing force, to achieve desirablesealability in a normal operating condition and effectively exhausthigh-pressure gas in a battery cell through a desired region, therebypreventing a possibility that the battery will catch fire or explode andthus improving the safety and operational reliability of the battery.

BACKGROUND OF THE INVENTION

As mobile devices have been increasingly developed, and the demand ofsuch mobile devices has increased, the demand of secondary batteries hasalso sharply increased as an energy source for the mobile devices. Amongthem is a lithium secondary battery having high energy density anddischarge voltage, on which much research has been carried out and whichis now commercially and widely used.

Generally, a secondary battery is manufactured by stacking or winding anelectrode assembly including a cathode, an anode, and a separatordisposed between the cathode and the anode, placing the electrodeassembly in a battery case formed of a metal container or a laminatesheet, and injecting an electrolyte into the battery case orimpregnating the electrode assembly with the electrolyte.

One of the principal problems to be solved in connection with thesecondary battery is to improve the safety of the secondary battery. Forexample, the secondary battery may explode by high temperature and highpressure which may be induced in the secondary battery due to theabnormal operation of the secondary battery, such as an internal shortcircuit, overcharge exceeding allowable current and voltage, exposure tohigh temperature, dropping, or deformation caused by external impact.Particularly for a pouch-shaped secondary battery, the sealing force ofa battery case lowers, with the result that an electrolyte may leak fromthe battery case.

FIG. 1 is an exploded perspective view typically illustrating thegeneral structure of a conventional representative pouch-shapedsecondary battery.

Referring to FIG. 1, the pouch-shaped secondary battery 10 includes anelectrode assembly 30, pluralities of electrode tabs 40 and 50 extendingfrom the electrode assembly 30, electrode leads 60 and 70 welded to theelectrode tabs 40 and 50, respectively, and a battery case 20 forreceiving the electrode assembly 30.

The electrode assembly 30 is a power generating element includingcathodes and anodes successively stacked while separators are disposedrespectively between the cathodes and the anodes. The electrode assembly30 may be constructed in a stacking structure or a stacking/foldingstructure. The electrode tabs 40 and 50 extend from correspondingelectrode plates of the electrode assembly 30. The electrode leads 60and 70 are electrically connected to the electrode tabs 40 and 50extending from the corresponding electrode plates of the electrodeassembly 30, respectively, for example, by welding. The electrode leads60 and 70 are partially exposed to the outside of the battery case 20.To upper and lower surfaces of the electrode leads 60 and 70 arepartially attached insulative films 80 for improving sealability betweenthe battery case 20 and the electrode leads 60 and 70 and, at the sametime, for securing electrical insulation between the battery case 20 andthe electrode leads 60 and 70.

The battery case 20 is formed of an aluminum laminate sheet. The batterycase 20 has a space defined therein for receiving the electrode assembly30. The battery case 20 is formed generally in the shape of a pouch.

The secondary battery 10 is manufactured by thermally welding contactregions at the outer circumference of the battery case 20 while theelectrode assembly 30 is mounted in the receiving space of the batterycase 20.

When the secondary battery is put in an abnormal operating condition,such as an internal short circuit, overcharge, or exposure to hightemperature, an electrolyte in the secondary battery is decomposed, withthe result that high-pressure gas is generated. The generatedhigh-pressure gas may deform the battery case and shorten the life spanof the secondary battery. Furthermore, the secondary battery may catchfire or explode due to the high-pressure gas. Therefore, it is preferredto separate thermally welded regions from each other, such that gas isexhausted outside through the separated regions, before the pressure ofthe secondary battery reaches a high-pressure level at which thesecondary battery may catch fire or explode. However, when gas noxiousto a human body is exhausted outside through an arbitrary region, it isdifficult to control the exhaust of the noxious gas.

Therefore, various attempts have been made to prevent the combustion orexplosion of a battery, when high-pressure gas is generated, andefficiently exhaust the gas outside.

As an example, Japanese Patent Application Publication No. 2006-185713discloses a secondary battery constructed in a structure in which upperand lower parts, of which the inner surfaces are made of a flexible,thermoplastic resin, of a battery case are overlapped, and flat portionsaround a power generating element receiving part are thermally welded,wherein a vertically bent concavo-convex part is partially formed in thethermally welded region.

In the above-described technology, the vertically bent concavo-convexpart serves to selectively exhaust high-pressure gas generated from theinterior of the battery case through the corresponding region. However,the disclosed secondary battery has a problem in that the thermallywelded flat portions around the vertically bent concavo-convex part areminutely deformed by the concavo-convex part, with the result that asealing force of the secondary battery decreases.

As another example, Japanese Patent Application Publication No.2005-116235 discloses a technology for forming a specific gas exhaustmechanism in a battery constructed in a structure in which the outercircumferential portions of a laminate film, in which an electrodeassembly is mounted, are thermally welded to seal the laminate film. Thedisclosed technology is to deform the innermost sealing layer of thelaminate film such that the innermost sealing layer has an adhesivestrength by thermal welding less than that of the remaining region ofthe laminate film using a method of partially removing a sealing layeror coupling a polymer resin exhibiting a low coupling force to some ofthe sealing layer.

In the method of partially removing the sealing layer, however, thesealing layer region and the region around the sealing layer arerelatively weak. As a result, internal gas may be concentrated on theseregions, even under the pressure generated in a state in which thebattery normally operates, and therefore, the regions may be easilyruptured. Consequently, it is difficult for the sealing layer to securesealability. In the method of coupling the polymer resin exhibiting thelow coupling force to some of the sealing layer, on the other hand,sealability at the interface between the different polymers may greatlylower due to the difference in material between the polymer resin of thesealing layer and the polymer resin exhibiting the low coupling force.

Although the above-described technologies may exhaust high-pressure gasthrough the selected region to secure safety, therefore, it is difficultto exhibit reliable sealability in a state in which the battery normallyoperates.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made to solve the aboveproblems, and other technical problems that have yet to be resolved.

As a result of a variety of extensive and intensive studies andexperiments to solve the problems as described above, the inventors ofthe present application have developed a secondary battery including anexhaust guide sealing portion formed at a sealing portion of a batterycase in a structure in which the width of the exhaust guide sealingportion decreases from the inside of the sealing portion toward theoutside of the sealing portion, the exhaust guide sealing portionexhibiting a low sealing force, and a bridge sealing portion formed atthe exhaust guide sealing portion, the bridge sealing portion exhibitinga relatively high sealing force, and have found that such a secondarybattery is capable of achieving desirable sealability in a normaloperating condition and effectively exhausting high-pressure gas in abattery cell through a desired region, thereby preventing a possibilitythat the battery will catch fire or explode and thus improving thesafety and operational reliability of the battery.

Specifically, an object of the present invention is to provide asecondary battery having a sealing portion of a specific structure toimprove the operational reliability and safety of the secondary battery.

In accordance with one aspect of the present invention, the above andother objects can be accomplished by the provision of a plate-shapedsecondary battery constructed in a structure in which an electrodeassembly of a cathode/separator/anode structure is mounted in a batterycase, and the battery case is sealed by thermal welding, wherein thebattery case is provided at a sealing portion around an electrodeassembly receiving part thereof with an exhaust guide sealing portionconfigured in a structure in which a width of the exhaust guide sealingportion decreases from an inside of the sealing portion toward anoutside of the sealing portion such that a sealing force of the exhaustguide sealing portion is first released, when high-pressure gas isgenerated in a battery cell, and therefore, the high-pressure gas isexhausted outside, the exhaust guide sealing portion being thermallywelded with a sealing force less than that of a sealing portion locatedat a remaining region (‘a remaining sealing portion’), and the batterycase is further provided at a middle of the exhaust guide sealingportion with a bridge sealing portion extending in parallel to theelectrode assembly for interconnecting opposite sides of the remainingsealing portion with a predetermined width, the bridge sealing portionbeing thermally welded with a sealing force greater than that of theexhaust guide sealing portion.

In the secondary battery according to the present invention, therefore,the sealing portion exhibits a desirable sealing force in a normaloperating condition of the battery. When high-pressure gas is generatedin the battery cell due to an abnormal operating condition of thebattery, on the other hand, the exhaust guide sealing portion isruptured earlier than the remaining region, with the result that thehigh-pressure gas is exhausted outside through the exhaust guide sealingportion. Consequently, it is possible to exhaust noxious gas to adesired place and to prevent a possibility that the battery will catchfire or explode.

The exhaust guide sealing portion is configured in a structure in whichthe width of the exhaust guide sealing portion decreases from the insideof the sealing portion toward the outside of the sealing portion suchthat an expansion stress caused by the high-pressure gas in the batterycell concentrates on the exhaust guide sealing portion. Consequently,when high-pressure gas is generated in the battery cell, the exhaustguide sealing portion is ruptured earlier than the remaining region toexhaust the gas.

The exhaust guide sealing portion may have a relatively small upper-end(outside) width equivalent to 10 to 50% of a relatively large lower-end(inside) width thereof. When the lower-end (inside) width of the exhaustguide sealing portion is too large, the sealing force of the battery ina normal operating condition may decrease. On the other hand, when thelower-end (inside) width of the exhaust guide sealing portion is toosmall, it is difficult to exhaust the gas to a desired degree.Consequently, the lower-end (inside) width of the exhaust guide sealingportion may be appropriately decided within the above-specified range.

In an exemplary example, the exhaust guide sealing portion may have alower-end (inside) width equivalent to 5 to 30% of the major-axis lengthof the battery case.

The shape of the exhaust guide sealing portion is not particularlyrestricted as long as the exhaust guide sealing portion is configured ina structure in which the width of the exhaust guide sealing portiondecreases from the inside of the sealing portion toward the outside ofthe sealing portion. For example, the exhaust guide sealing portion maybe formed in a horizontal plane shape of at least one selected from agroup consisting of a semicircle, a triangle, and a trapezoid.Preferably, the exhaust guide sealing portion is formed in thetrapezoidal shape.

The bridge sealing portion effectively increases the sealing force ofthe sealing portion 310, which may be weakened by the formation of theexhaust guide sealing portion. That is, the expansion stress caused bythe high-pressure gas in the battery cell concentrates on the exhaustguide sealing portion; however, since the bridge sealing portion isruptured only by gas pressure at which the exhaust of gas is required,it is possible to reliably secure the operation of the battery.

As previously defined, the bridge sealing portion may exhibit a sealingforce greater than that of the exhaust guide sealing portion and equalto, less than, or greater than that of the remaining sealing portion. Inan exemplary example, the bridge sealing portion may exhibit a sealingforce 30 to 100% greater than that of the exhaust guide sealing portion.

When the width of the bridge sealing portion is too large, the exhaustof high-pressure gas generated in the battery may be disturbed. On theother hand, when the width of the bridge sealing portion is too small,the sealing portion may be easily weakened even by low-pressure gas.Preferably, therefore, the bridge sealing portion has a width equivalentto 10 to 60% of that of the remaining sealing portion.

According to circumstances, the battery case may be further provided atan interface between the exhaust guide sealing portion and the remainingsealing portion with an interface sealing portion thermally welded witha sealing force greater than that of the remaining sealing portion.

The interface sealing portion prevents a possibility that the sealingforce of the region around the exhaust guide sealing portion will beweakened by the formation of the exhaust guide sealing portion. Also,when high-pressure gas is generated in the battery, the interfacesealing portion prevents the deformation and release in the sealingforce of the exhaust guide sealing portion and the remaining sealingportion adjacent to the exhaust guide sealing portion, during theexhaust of gas, thereby guiding the gas to the exhaust guide sealingportion with higher reliability.

In the above-described structure, the width of the interface sealingportion may be changed as needed. For example, the interface sealingportion may have a width equivalent to 2 to 20% of that of the remainingsealing portion.

In an exemplary example, the interface sealing portion may have asealing force 30 to 150% greater than that of the remaining sealingportion. At this time, the sealing force of the bridge sealing portionmay be less than that of the interface sealing portion. According tocircumstances, however, the sealing force of the bridge sealing portionmay be equal to that of the interface sealing portion.

The location of the exhaust guide sealing portion is not particularlyrestricted. For example, the location of the exhaust guide sealingportion may be appropriately decided according to a desired gas exhaustroute. That is, a predetermined exhaust member may be mounted to thebattery cell itself or a pack case to prevent noxious internal gas frombeing unintentionally exhausted out of the battery cell, and thelocation of the exhaust guide sealing portion may be decided such thatthe exhaust guide sealing portion communicates with the exhaust member.

In an exemplary example, the exhaust guide sealing portion may be formedat the middle of each of opposite-side sealing portions located on theminor axis of the battery case on the basis of the middle of the batterycase. Here, the middle of the battery case means the intersectionbetween the middle of the major axis and the middle of the minor axis ofthe battery case and its surrounding region. The middle of the batterycase is a region where the gas flowing route is the shortest in thebattery, and the expansion in volume of the battery case is thegreatest, and therefore, it is possible to rapidly and efficientlyachieve the exhaust of gas.

The battery case is preferably applicable to a secondary batteryconstructed in a structure in which an electrode assembly is mounted ina pouch-shaped case formed of a laminate sheet, particularly an aluminumlaminate sheet, including a resin layer and a metal layer.

The laminate sheet includes an outer coating layer formed of polymerfilm, a barrier layer formed of metal foil, and an inner sealant layerformed of a polyolefin-based material. It is required for the outercoating layer to exhibit excellent resistance to an externalenvironment, and therefore, the outer coating layer must exhibit apredetermined tensile strength and weather resistance. In this aspect,oriented nylon film or polyethylene terephthalate (PET) are preferablyused as the polymer resin for the outer coating layer. The barrier layermay be made of, preferably, aluminum to prevent the introduction orleakage of foreign matter, such as gas or moisture and increase thestrength of the battery case. The inner sealant layer may be made of,preferably, a polyolefin-based material exhibiting a high thermalwelding property (a thermal adhesion property), a low hygroscopicproperty to restrain the penetration of an electrolyte, and a propertywhich is not expanded or corroded by the electrolyte, more preferablycast polypropylene (cPP).

The structure of the electrode assembly is not particularly restrictedso long as the electrode assembly is constructed in a structure in whichthe electrode assembly includes a cathode, an anode, and a separatordisposed between the cathode and the anode. For example, the electrodeassembly may be constructed in a folding, stacking, or stacking/foldingtype structure. The details of the stacking/folding type electrodeassembly are disclosed in Korean Patent Application Publication No.2001-0082058, No. 2001-0082059, and No. 2001-0082060, which have beenfiled in the name of the applicant of the present patent application.The disclosures of the above-mentioned patent publications are herebyincorporated by reference as if fully set forth therein.

The secondary battery according to the present invention may be,preferably a lithium secondary battery. In particular, the secondarybattery according to the present invention is preferably applied to aso-called a lithium ion polymer battery having an electrode assemblyimpregnated with a lithium-containing electrolyte in the form of a gel.

In accordance with another aspect of the present invention, there isprovided a middle- or large-sized battery module including the secondarybattery as a unit cell.

In particular, the secondary battery according to the present inventionis preferably used in a high-power, large-capacity battery requiring along-term life span and excellent durability or a middle- or large-sizedbattery module and a middle- or large-sized battery pack including aplurality of such batteries as unit cells. The middle- or large-sizedbattery module may be used as a power source for, for example, electricvehicles, hybrid electric vehicles, electric motorcycles, and electricbicycles.

The structures of the middle- or large-sized battery module and themiddle- or large-sized battery pack and a method of manufacturing thesame are well known in the art to which the present invention pertains,and a detailed description thereof will not be given.

In accordance with a further aspect of the present invention, there isprovided a method of manufacturing the secondary battery, the methodincluding mounting the electrode assembly in the receiving part of thebattery case and thermally welding the sealing portion at the outercircumference of the battery case on a heating jig formed in an engravedshape corresponding to the exhaust guide sealing portion, the bridgesealing portion, and/or the interface sealing portion and having a depthinversely proportional to sealing forces of the sealing portions.

The thermal welding for forming the sealing portion is achieved bysimultaneously heating and pressurizing a portion to be sealed (forexample, the outer circumference of the battery case). The sealing forceis generally in proportion to a pressurizing force for thermal welding.Consequently, the smaller the engraved depth of heating jig is, thehigher the sealing force of the sealing portion corresponding to theheating jig may be.

In the manufacturing method according to the present invention,therefore, it is possible to simultaneously form a desired exhaust guidesealing portion, bridge sealing portion, and interface sealing portionby only the engraved depth. Consequently, the present invention may beapplicable to a conventional manufacturing process as long as theheating jig is modified.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is an exploded perspective view illustrating the generalstructure of a conventional pouch-shaped secondary battery;

FIG. 2 is a see-through sectional view illustrating a secondary batteryhaving an exhaust guide sealing portion according to an embodiment ofthe present invention;

FIG. 3 is an enlarged horizontal sectional view typically illustrating Bregion of FIG. 2;

FIG. 4 is a horizontal sectional view typically illustrating an exhaustguide sealing portion according to another embodiment of the presentinvention; and

FIG. 5 is a vertical sectional view typically illustrating heating jigsand a battery case, corresponding to C-C region, to form the exhaustguide sealing portion of FIG. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Now, exemplary embodiments of the present invention will be described indetail with reference to the accompanying drawings. It should be noted,however, that the scope of the present invention is not limited by theillustrated embodiments.

FIG. 2 is a see-through sectional view illustrating a secondary batteryhaving an exhaust guide sealing portion according to an embodiment ofthe present invention, and FIG. 3 is an enlarged horizontal sectionalview typically illustrating B region of FIG. 2.

Referring to these drawings, the secondary battery 100 includes anelectrode assembly 320, a battery case for receiving the electrodeassembly 320, and two electrode leads 420 and 421 electrically connectedto electrode tabs of the electrode assembly 320.

The two electrode leads 420 and 421 are electrically connected to theelectrode tabs (not shown), extending from corresponding electrodeplates of the electrode assembly 320, by welding. The two electrodeleads 420 and 421 are partially exposed to the outside of the batterycase 300. To upper and lower surfaces of the electrode leads 420 and 421are attached insulative films 430 for improving sealability between thebattery case 300 and the electrode leads 420 and 421 and, at the sametime, for securing electrical insulation between the battery case 300and the electrode leads 420 and 421. The two electrode leads 420 and421, constituting a cathode and an anode, may be arranged in oppositedirections as shown in the drawings. Alternatively, the two electrodeleads 420 and 421 may be arranged side by side in the same direction.

The battery case 300 is formed of an aluminum laminate sheet. Thebattery case 300 has a receiving part defined therein for receiving theelectrode assembly 320. At a sealing portion 310 around the receivingpart, an upper battery case and a lower battery case are coupled to eachother by welding, with the result that the battery case 300 is formedgenerally in the shape of a pouch.

The sealing portion 310 has an exhaust guide sealing portion 200 whichis formed in the shape of a trapezoid, i.e., in a structure in which thewidth of the exhaust guide sealing portion 200 decreases from the insideof the sealing portion 310 toward the outside of the sealing portion310. When gas is generated in the battery, the battery case 300 swellsthe most greatly at the middle region M, with the result that adeformation force is the greatest at opposite-side sealing portions 310located on the minor axis S of the battery case 300. Consequently, theexhaust guide sealing portion 200 is formed at the middle region of eachof the opposite-side sealing portions 310 located on the minor axis S ofthe battery case 300 on the basis of the middle M of the battery case300. As a result, the exhaust guide sealing portion 200 is firstruptured due to internal pressure created by the internal gas of thebattery, with the result that the sealability of the battery isreleased, and therefore, the internal gas is exhausted out of thebattery cell through the ruptured exhaust guide sealing portion 200.

The exhaust guide sealing portion 200 has a lower-end (inside) width Tequivalent to approximately 10% of a major-axis length L of the batterycase 300. The exhaust guide sealing portion 200 has an upper-end(outside) width t equivalent to approximately 40% of the lower-end(inside) width T.

At the middle of the exhaust guide sealing portion 200 is formed abridge sealing portion 210 extending in parallel to the electrodeassembly (not shown) for interconnecting opposite sides of the sealingportion 310 with a width E.

The bridge sealing portion 210 may exhibit a sealing force greater thanthat of the exhaust guide sealing portion 200 and equal to, less than,or greater than that of the sealing portion 310.

The bridge sealing portion 210 effectively increases the sealing forceof the sealing portion 310, which may be weakened by the formation ofthe exhaust guide sealing portion 200. Since the bridge sealing portion210 is ruptured only by gas pressure at which the exhaust of gas isrequired, it is possible to reliably secure the operation of thebattery.

The width E of the bridge sealing portion 210 is equivalent toapproximately 25% of the width W of the sealing portion 310.

In the drawing, meanwhile, the electrode leads 420 and 421 protrudeoutward from opposite-side sealing portions 310 located on the majoraxis L on the basis of the middle M of the battery case 300. That is, itis required for the regions where the electrode leads 420 and 421 arelocated to maintain high sealability and insulation, and therefore, itis preferred to form the bridge sealing portion 210 at a regiondifferent from the regions where the electrode leads 420 and 421 arelocated.

FIG. 4 is a horizontal sectional view typically illustrating an exhaustguide sealing portion according to another embodiment of the presentinvention.

Referring to FIG. 4, an interface sealing portion 220 is formed at theinterface between the bridge sealing portion 210 and the sealing portion310. The interface sealing portion 220 exhibits a sealing force greaterthan that of the sealing portion 310. According to circumstances, asshown in FIG. 4, the sealing force of the interface sealing portion 220may be equal to that of the bridge sealing portion 210.

The interface sealing portion 220 prevents a possibility that thesealing force of the region around the interface sealing portion 220will weaken due to the formation of the exhaust guide sealing portion200. Also, when high-pressure gas is generated in the battery, theinterface sealing portion 220 prevents the deformation of the sealingportion 310 adjacent to the exhaust guide sealing portion 200 and therelease of the sealing force, during the exhaust of the gas.Consequently, it is possible for the interface sealing portion 220 toguide the exhaust of the gas through the exhaust guide sealing portion200 with higher reliability.

The interface sealing portion 220 has a width D equivalent toapproximately 15% of the width W of the sealing portion 310.

FIG. 5 is a vertical sectional view typically illustrating heating jigsand a battery case, corresponding to C-C region, to form the exhaustguide sealing portion of FIG. 4.

Referring to FIG. 5, an upper sheet 301 and a lower sheet 302 of thebattery case are heated and pressurized by a pair of heating jigs 500and 501 such that the upper sheet 301 and the lower sheet 302 arethermally welded to each other.

At the surface of the upper heating jig 500 is formed an engravedstructure 510 corresponding to the sealing portion 310, the exhaustguide sealing portion 200, and the interface sealing portion 220. Theengraved structure 510 may be formed at the surface of the lower heatingjig 501. Alternatively, the engraved structure 510 may be formed notonly at the surface of the upper heating jig 500 but also at the surfaceof the lower heating jig 501.

The engraved depth of the engraved structure 510 is in inverseproportion to the sealing force of the sealing portion. That is, on thebasis of the depth of the region corresponding to the interface sealingportion 220, the depth t_(a) corresponding to the exhaust guide sealingportion 200 is the greatest, and the depth t_(b) corresponding to thesealing portion 310 is not greater than the depth t_(a) corresponding tothe exhaust guide sealing portion 200. During thermal welding,therefore, the least pressure is applied to the exhaust guide sealingportion 200, with the result that the sealing force of the exhaust guidesealing portion 200 is relatively low, whereas the greatest pressure isapplied to the interface sealing portion 220, with the result that thesealing force of the interface sealing portion 220 is relatively high.

Consequently, it is possible to easily manufacture the structure of FIG.4 using the upper heating jig 500 having the engraved structure 510.

Hereinafter, an example of the present invention will be described inmore detail. It should be noted, however, that the scope of the presentinvention is not limited by the illustrated example.

Example 1

A cathode was manufactured by coating slurry including lithium cobaltoxide, PVdF, and a conducting agent mixed according to a generally knowncomposition on an aluminum current collector. An anode was manufacturedby coating slurry including graphite, PVdF, and a conducting agent mixedaccording to a generally known composition on a copper currentcollector.

Between the cathode and the anode was disposed a separator which hadbeen cut into a size somewhat greater than that of the cathode and theanode to manufacture an electrode assembly. The electrode assembly wasmounted between an upper case and a lower case, each having a receivingpart, of a pouch-shaped battery case formed of a laminate sheet.

The laminate sheet was configured in a structure including an insideresin layer made of cast polypropylene (cPP), an insulative aluminummetal layer, and an outside resin layer made of polyethyleneterephthalate (PET).

Sealing portions formed around the receiving parts of the upper case andthe lower case were placed on the heating jigs of FIG. 5, and werecoupled to each other by thermal welding. An exhaust guide sealingportion was formed at the sealing portions such that the exhaust guidesealing portion has a relatively small upper-end (outside) widthequivalent to 40% of a relatively large lower-end (inside) width of theexhaust guide sealing portion. A bridge sealing portion was formed suchthat the bridge sealing portion had a width equivalent to 25% of that ofthe remaining sealing portion. An interface sealing portion was formedsuch that the interface sealing portion had a width equivalent to 15% ofthat of the remaining sealing portion. Thermal welding was carried outsuch that the exhaust guide sealing portion had a sealing forceequivalent to approximately 60% of that of the remaining sealingportion, and the bridge sealing portion and the interface sealingportion had a sealing force equivalent to 120% of that of the remainingsealing portion.

Comparative Example 1

A secondary battery was manufactured in the same manner as Example 1except that no exhaust guide sealing portion was formed at the secondarybattery.

Comparative Example 2

A secondary battery was manufactured in the same manner as Example 1except that neither a bridge sealing portion nor an interface sealingportion was formed at the secondary battery.

Experimental example 1

200-cycle charge and discharge were carried out on 30 batteriesmanufactured according to Example 1 and Comparative examples 1 and 2 onconditions of 4.3 V charge and 3.0 V discharge to confirm whether gaswas exhausted from the batteries or not.

Also, the batteries were placed in a chamber having an internaltemperature of approximately 90 degrees, such that the batteriesswelled, to confirm whether the batteries caught fire or exploded, theexhaust direction of internal gas, and battery swelling deviation duringthe exhaust of gas. The exhaust direction was decided by the number ofsealing portions ruptured when the internal gas was exhausted. That is,the exhaust direction was set to be 1 when the sealing portion locatedat the same position of all the batteries was ruptured. When the sealingportions located at the different positions of some batteries wereruptured, the number of the ruptured sealing portions was added. Also,the battery swelling deviation during the exhaust of gas was convertedinto a percentage of the thickness of the battery exhibiting the minimumswelling degree during the exhaust of gas to the thickness of thebattery exhibiting the maximum swelling degree during the exhaust ofgas.

TABLE 1 Number of Battery batteries from Number of Exhaust swellingwhich gas was batteries which direction deviation exhausted caught fireor of inter- during ex- after 200 cycles exploded nal gas haust of gasExample 1 0 0 1 8 Comparative 0 7 8 32 example 1 Comparative 8 0 1 13example 2

It can be seen from Table 1 that gas was not exhausted from all thebatteries of Example 1 in a normal operating condition, and, even whenthe batteries swelled in a high temperature condition, the batteries didnot catch fire or explode by the effective exhaust of internal gas fromthe batteries. Also, the internal gas of the batteries was exhausted inone direction or in two directions.

On the other hand, it was confirmed that a great number of the batteriesof Comparative example 1 caught fire or exploded. Also, it was confirmedthat the regions ruptured during the exhaust of the internal gaschanged.

It is also confirmed that, although the batteries of Comparative example2 did not catch fire or explode by the effective exhaust of internal gasfrom the batteries swelled in a high temperature condition, gas wasexhausted from a great number of the batteries in a normal operatingcondition.

INDUSTRIAL APPLICABILITY

As apparent from the above description, the secondary battery accordingto the present invention is capable of exhibiting a high sealing forcein a normal operating condition, and first releasing a sealing force ofthe exhaust guide sealing portion, when high-pressure gas is generatedin the battery cell to selectively exhaust the high-pressure gas througha desired region. Consequently, the present invention has the effect ofpreventing a possibility that the battery will catch fire or explode,thereby considerably improving the safety of the battery and solvingproblems caused by indiscreet exhaust of noxious gas. Furthermore, theexhaust guide sealing portion is easily manufactured using predeterminedheating jigs during the manufacture of the battery, thereby not causingthe increase in manufacturing costs of the battery.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A plate-shaped secondary battery constructed in a structure in whichan electrode assembly of a cathode/separator/anode structure is mountedin a battery case, and the battery case is sealed by thermal welding,wherein the battery case is provided at a sealing portion around anelectrode assembly receiving part thereof with an exhaust guide sealingportion configured in a structure in which a width of the exhaust guidesealing portion decreases from an inside of the sealing portion towardan outside of the sealing portion such that a sealing force of theexhaust guide sealing portion is first released, when high-pressure gasis generated in a battery cell, and therefore, the high-pressure gas isexhausted outside, the exhaust guide sealing portion being thermallywelded with a sealing force less than that of a sealing portion locatedat a remaining region (‘a remaining sealing portion’), and the batterycase is further provided at a middle of the exhaust guide sealingportion with a bridge sealing portion extending in parallel to theelectrode assembly for interconnecting opposite sides of the remainingsealing portion with a predetermined width, the bridge sealing portionbeing thermally welded with a sealing force greater than that of theexhaust guide sealing portion; and the exhaust guide sealing portion hasa lower-end (inside) width equivalent to 5 to 30% of a major-axis lengthof the battery case.
 2. The secondary battery according to claim 1,wherein the exhaust guide sealing portion has a relatively smallupper-end (outside) width equivalent to 10 to 50% of a relatively largelower-end (inside) width thereof.
 3. (canceled)
 4. The secondary batteryaccording to claim 1, wherein the exhaust guide sealing portion isformed in a horizontal plane shape of at least one selected from a groupconsisting of a semicircle, a triangle, and a trapezoid.
 5. Thesecondary battery according to claim 4, wherein the exhaust guidesealing portion is formed in the trapezoidal shape.
 6. The secondarybattery according to claim 1, wherein the bridge sealing portion has awidth equivalent to 10 to 60% of that of the remaining sealing portion.7. The secondary battery according to claim 1, wherein the battery caseis further provided at an interface between the exhaust guide sealingportion and the remaining sealing portion with an interface sealingportion thermally welded with a sealing force greater than that of theremaining sealing portion.
 8. The secondary battery according to claim7, wherein the interface sealing portion has a width equivalent to 2 to20% of that of the remaining sealing portion.
 9. The secondary batteryaccording to claim 1, wherein the exhaust guide sealing portion isformed at a middle of one side or each side sealing portion located on aminor axis of the battery case on the basis of a middle of the batterycase.
 10. The secondary battery according to claim 1, wherein thebattery case is formed of a laminate sheet including a resin layer and ametal layer.
 11. The secondary battery according to claim 10, whereinthe sheet is an aluminum laminate sheet.
 12. The secondary batteryaccording to claim 1, wherein the electrode assembly is constructed in afolding, stacking, or stacking/folding type structure.
 13. The secondarybattery according to claim 1, wherein the battery is a lithium ionpolymer battery.
 14. A middle- or large-sized battery module comprisingthe secondary battery according to claim 1, as a unit cell.
 15. A methodof manufacturing the secondary battery according to claim 1, the methodcomprising: mounting the electrode assembly in the receiving part of thebattery case; and thermally welding the sealing portion at the outercircumference of the battery case on a heating jig formed in an engravedshape corresponding to the exhaust guide sealing portion, the bridgesealing portion, and/or the interface sealing portion and having a depthinversely proportional to sealing forces of the sealing portions.